(function (doc, win) { 
	var docEl = doc.documentElement, 
		resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize', 
		recalc = function () {
			var clientWidth = docEl.clientWidth;
			if(!clientWidth) return; 
			if(clientWidth>=640){ 
				docEl.style.fontSize = '100px'; 
			}else{ 
				docEl.style.fontSize = 100 * (clientWidth / 640) + 'px'; 
			} 
		}; 
		if (!doc.addEventListener) return; 
		win.addEventListener(resizeEvt, recalc, false); 
		doc.addEventListener('DOMContentLoaded', recalc, false); 
})(document, window);